In recent years, it has become increasingly necessary to provide improved mufflers for the attenuation of the exhaust noise produced by internal combustion engines used in transportation vehicles, due to public outcry and the resulting government regulations. New regulations are almost continually being proposed which require ever more stringent noise standards.
Many types of exhaust systems utilizing combinations of headers, collectors, and mufflers, as well as other noise reducing devices have been developed to address this problem. One type of exhaust system, generally referred to as a collector, combines and directs exhaust gases from separate exhaust tubes into a common downstream exhaust pipe. An exhaust muffler is attached downstream of the outlet pipe of the collector to effect noise reduction of the exhaust gases. Additionally, a catalytic converter may be attached to the exhaust system to convert some of the pollutants of the exhaust gases into harmless compounds. Unfortunately, such collector/muffler/catalytic converter systems are not very effective at minimizing the complexity of the exhaust system due to their many separate components. Moreover, they create back pressure which results in reduced performance of the engine. This reduced performance, or reduced horsepower, is undesirable in most vehicles.
Some muffler systems include sound attenuating material disposed in an space defined by an interior casing, or a tube structure, and an outer casing of the muffler. Holes or perforations in the interior casing, or tube structure, provide paths for the transmission of reflected high frequency components of noise into the sound attenuating material so that the noise can be subsequently dissipated. Unfortunately, this sound absorbing material adds to the overall weight of the muffler system, restricts the flow of exhaust, and provides a medium for the buildup of heat.
Thus, what is needed is An exhaust muffler that is lightweight, inexpensive, durable under attack of hot and corrosive exhaust gases, and impervious to vibration. Moreover, what is needed is An exhaust muffler that provides efficient noise attenuation while not causing undue back pressure to the engine, that is, one that provides good muffling without degrading engine performance.